Generator conversion to 12V Polarity?

C

Cartravel

Senior Member
I've tried to check the archives. There is a lot of discussion on this subject, but I haven't found an answer to my question. I'm going with 12v on my '41 pickup project. I have purchased the 12v field coils and installed them in the generator case. I've set up a test stand using an old motor set up next to an intake manifold.

To test it, I put a voltmeter on the armature terminal and spin the generator. I believe I should see a small positive voltage and then I should be able to touch the field to the armature terminal and see the voltage increase. The problem is I'm getting either no voltage or a negative voltage. I believe it must have to do with polarity of the fields. I'm thinking either the field coils or pole pieces need to be switched around. If I take the armature out, I find that with the residual magnetism, the south pole points towards the field terminal side. If I apply current to the fields, the polarity switches around. When I remove the current it goes back to the original state. I'd think the polarity should run the same direction in both cases, but don't know which way it should be. Can someone tell me how to get this working?
Thanks,
Larry Young
 
http://www.fordbarn.com/forum/showthread.php?t=71055

This article seems to address the question for 3 brush generators. Does it apply to a 2 brush. As I mentioned I have applied voltage, but it didn't change the polarity of the residual magnetism (I thought it should). Maybe the problem is in the armature. I don't have access to a growler, so can only do resistance tests. The resistances between the commutator segment are very low and difficult to measure, but none are grounded.
 
If you motor the generator it should turn in the same direction as
it would when when driven by the engine.

Bob
 
Take Bob C advice and motor it.
If it doesnt run like it should then start tracking down the problem.
Just swapping parts isnt the best way to find a fault.
 
I was getting nothing out of that first armature, so I changed it. Then I ran it as a motor and it rotated the same as in engine. I then spun it with an electric motor (same direction as in car) and found it was generating negative voltage. I switched the leads on the field coils and now everything is working fine. I had not realized it would make a difference. I thought NSNSNS.... would be the same as SNSNSN.... I guess not. I've never seen directions on how to install the field coils, except for the 3 brush generators.
Larry Young
 

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